In kotlin how to use ViewModel With ViewModelProvider.AndroidViewModelFactory?

Question

In my current project I use the next line:

mViewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)

For instance a ViewModel but in https://developer.android.com/reference/android/arch/lifecycle/ViewModelProviders.html#ViewModelProviders() recommend use ViewModelProvider.AndroidViewModelFactory because ViewModelProviders() was deprecated in API level 1.1.0.

any idea for this purpose?

Answer 1

If you had a simple ViewModel extending AndroidViewModel without any additional constructor parameters, its as follows

1. Extend AndroidViewModel without any additional constructor parameters

class FooViewModel(application: Application) : AndroidViewModel(application) {}

2. Create View Model in Activity

val viewModel = ViewModelProvider(this).get(FooViewModel::class.java)

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But if you had a ViewModel extending AndroidViewModel with any additional constructor parameters, its as follows

1. Extend AndroidViewModel with any additional constructor parameters

class FooViewModel(application: Application, foo: Foo) : AndroidViewModel(application) {}

2. Create a new view model factory extending ViewModelProvider.AndroidViewModelFactory

class FooViewModelFactory(val application: Application, val foo: Foo): ViewModelProvider.AndroidViewModelFactory(application) {

            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                return FooViewModel(
                    application, foo
                ) as T
            }

     }

3. Create View Model in Activity

val viewModel = ViewModelProvider(this, FooViewModelFactory(application, foo)).get(FooViewModel::class.java)

Answer 2

EDIT: The original question is now irrelevant, as you should no longer use the ViewModelProviders utility class. Instead, you should create a ViewModelProvider instance like so:

val viewModel = ViewModelProvider(thisFragment).get(MyViewModel::class.java)

Original answer below.

---

ViewModelProviders is just a utility class with static methods, there's no need to instantiate it (there are no instance methods in it anyway), so the constructor being deprecated shouldn't be a concern.

The way you use it is by calling its appropriate of method for your use case, passing in a Fragment or Activity, and then calling get on the ViewModelProvider it returns:

val viewModel = ViewModelProviders.of(thisFragment).get(MyViewModel::class.java)

If you don't provide your own factory in the second parameter of the of method, AndroidViewModelFactory will be used by default. This implementation can either create ViewModel subclasses that have no constructor parameters, or ones that extend AndroidViewModel, like such:

class MyViewModel(application: Application) : AndroidViewModel(application) {

    // use application

}